This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-068079, filed Mar. 15, 1999; and No. 11-073065, filed Mar. 18, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a plasma processing method and a plasma processing apparatus for processing a subject using plasma generated by applying a voltage between upper and lower electrodes.
In a plasma processing apparatus of a parallel-plate type, as a wafer increases in diameter, it is required that plasma be uniformed in order to make the thickness of the wafer more uniform within the wafer plane and plasma is increased in density between upper and lower electrodes in order to make plasma processing more efficient.
In the parallel-plate type plasma processing apparatus having large electrodes to form a film on the large-diameter wafer, however, pressure and plasma density are varied with a distance between the upper and lower electrodes. The apparatus therefore has a problem where in-plane uniformity of plasma processing (uniformity of deposition temperature and deposition quality in CVD, that of etching rate and etching shape in etching, etc.) cannot be obtained sufficiently even by controlling pressure, an electrode-to-electrode interval, a gas flow rate, and the like.
FIG. 1 is a general view showing a structure of a prior art plasma processing apparatus. Referring to FIG. 1, a reaction chamber 1 includes a vacuum outlet 11 to allow plasma processing under a reduced pressure. An upper electrode 3 has a gas pipe 4 for introducing gas and serves as a plurality of gas introducing inlets (dispersion nozzles) 5. A high-frequency power supply (not shown) is connected to the upper electrode 3. A silicon wafer 7, which is a subject to be processed, is placed on a support table 2 including a resistance heating heater 8 for controlling the temperature of the wafer 7. The high-frequency power supply (not shown) is connected to the support table 2. A magnet (not shown) is provided outside the chamber 1 to generate a magnetic field on the wafer 7 and increase the density of discharged plasma.
Using the above-described plasma processing apparatus, a silicon oxide thin film containing fluorine is deposited on a silicon wafer through the following process. First, the reaction chamber 1 is evacuated by the vacuum outlet 11, and then the wafer 7 is put on the support table 2 and heated to a desired temperature of 370xc2x0 C. using the heater 8. After that, SiF4 of 25 cc/min (scum) and O2 of 50 cc/min (scum) are introduced as gas materials into the chamber 1 through the gas inlets 5, and a high-frequency voltage of 27.12 MHz is applied to the upper electrode 3 using the high-frequency power supply (not shown) to discharge plasma. The silicon oxide film is thus completed. In this process, the internal pressure of the chamber 1 is 4 Pa and the intensity of the magnet is 120 Gauss. A high-frequency voltage of 13.56 MHz is applied to the support table 2 using the high-frequency power supply. All the gas inlets 5 of the upper electrode 3 have the same shape. In the prior art parallel-plate type plasma processing apparatus, however, high-density plasma is concentrated near the upper electrode 3. If, therefore, gas such as SiF4, which is harder to discharge than O2, is employed, it cannot be decomposed sufficiently in the above high-density plasma concentrating area, with the result that a uniform discharge is difficult to obtain, and neither uniformity of thickness nor that of fluorine (F) concentrations can be obtained within the plane of the large-diameter wafer.
In the prior art plasma processing apparatus described above, since all the gas inlets have the same shape, high-density plasma is concentrated near the upper electrode. Therefore, when gas, which is hard to discharge, is used, it is not decomposed sufficiently and the speed of plasma processing is decreased.
The present invention has been developed in order to resolve the above problem and its object is to provide a plasma processing method and a plasma processing apparatus which increase in plasma processing speed.
Another object of the present invention is to provide a plasma processing method and a plasma processing apparatus which improve in in-plane uniformity of plasma processing speed.
According to a first aspect of the present invention, there is provided a plasma processing method comprising: applying a voltage between a lower electrode on which a subject to be processed is placed and an upper electrode opposed to the lower electrode and including a plurality of gas introducing inlets facing the lower electrode, at least some of the inlets being expanded in a diameter direction at open ends thereof; introducing a material gas from the inlets to generate plasma; and processing the subject using the plasma.
According to a second aspect of the present invention, there is provided a plasma processing method comprising: applying a voltage between a lower electrode on which a subject to be processed is placed and an upper electrode opposed to the lower electrode and including a plurality of gas introducing inlets facing the lower electrode to generate plasma, an interval between the lower electrode and open ends of the plurality of inlets being varied with an in-plane position of the upper electrode; and processing the subject using the plasma.
According to a third aspect of the present invention, there is provided a plasma processing method of processing a subject using plasma generated by applying a voltage between a lower electrode on which the subject is placed and an upper electrode opposed to the lower electrode and including a plurality of gas inlets facing the lower electrode, wherein a shield plate having a plurality of holes is disposed between the upper electrode and the lower electrode.
According to a fourth aspect of the present invention, there is provided a plasma processing apparatus of a parallel-plate type comprising a lower electrode on which a subject to be processed is placed and an upper electrode opposed to the lower electrode and having a plurality of gas inlets facing the lower electrode, wherein at least some of the plurality of gas inlets are expanded in a diameter direction at open ends thereof.
According to a fifth aspect of the present invention, there is provided a plasma processing apparatus of a parallel-plate type comprising a lower electrode on which a subject to be processed is placed and an upper electrode opposed to the lower electrode and having a plurality of gas inlets facing the lower electrode, wherein an interval between the lower electrode and open ends of the plurality of inlets is varied with an in-plane position of the upper electrode.
According to a sixth aspect of the present invention, there is provided a plasma processing apparatus of a parallel-plate type comprising a lower electrode on which a subject to be processed is placed and an upper electrode opposed to the lower electrode and having a plurality of gas inlets facing the lower electrode, wherein a shield plate having a plurality of holes is disposed between the upper electrode and the lower electrode.
In one aspect of the present invention, since at least some of plural gas introducing inlets are formed in the upper electrode such that their open ends are expanded in their diameter directions, a high-density plasma region, which is formed when plasma is discharged, can be broadened. Consequently, the high-density plasma region is not concentrated near the upper electrode, but increases gas dissociation efficiency and improves a plasma processing rate.
When at least two different gases are introduced, the open end of an inlet for introducing gas whose dissociation efficiency is low in plasma is expanded in its diameter direction more greatly than that of an inlet for introducing gas whose dissociation efficiency is high. The gas having a low dissociation efficiency in plasma can thus be promoted in dissociation.
Since, moreover, the open ends of the gas introducing inlets are varied in diameter with an in-plane position of the upper electrode, not only the plasma processing rate can be improved, but also the distribution characteristics of the plasma processing rate can be controlled. Since, in particular, the diameters of the inlets in the outer region are set larger than that in the center of the upper electrode, the plasma processing rate can be uniformed.
In another aspect of the present invention, a distance between the lower electrode and the open ends of the plural gas introducing inlets is varied with an in-plane position of the upper electrode, so that the distribution characteristics of plasma processing rate can be controlled. Since, in particular, the distance in the outer region of the upper electrode is set shorter than that in the center thereof, the plasma processing rate can be uniformed.
In still another aspect of the present invention, since a shield plate having a plurality of holes is disposed between the upper and lower electrodes, gas whose dissociation efficiency is relatively low is introduced from the high-density plasma region into the low-density plasma region, and collides with the shield plate and returns to the high-density plasma region, thereby promoting the dissociation of the gas. Consequently, the entire apparatus is improved in plasma processing rate.
Moreover, the holes of the shield plate are aligned with only the orbit in which the gas having relatively high dissociation efficiency goes straight and the shield plate blocks the orbit in which the gas having relatively low dissociation efficiency goes straight, so that the plasma processing rate is increased.
Furthermore, the holes of the shield plate are varied in number with an in-plane position of the upper electrode, a plasma region can be formed in accordance with the in-plane position, and not only the plasma processing rate can be improved but also the distribution characteristics of plasma processing rate can be controlled. Since, in particular, the density of holes of the shield plate in the outer region of the upper electrode is set higher than that in the center thereof, the plasma processing rate can be uniformed.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.